This invention relates to modifications to friction discs utilized in wet disc brakes to address noise, heat transfer and vibration issues.
Wet disc friction brakes are utilized to stop many vehicles. This type of brake is also used in many other non-vehicle applications. Generally, a wet disc friction brake includes a plurality of rotating discs fixed to an inner rotating member which rotates with the wheel, and a plurality of interspaced discs fixed to a stationary housing member. Typically, the rotating discs are provided with friction material. The piston is normally biased out of contact with the rotating and stationary discs by a spring bias force. A hydraulic chamber is selectively supplied with a pressurized fluid to bias a piston against the spring force and to collapse the rotating and stationary discs together. As the discs collapse together, they engage each other and the friction created between the discs reduces rotation of the rotating member relative to the stationary member.
One challenge with regard to the design of the discs in the wet friction brake environment, occurs when the frequency of the disc brake assemblies approximates the frequencies of the axles which carry the disc brake assemblies. When such a combination occurs, during deceleration, both the axle and the disc brake assembly have sometimes both reached their resonant frequency. At that time, a vehicle may experience vibrating and/or noise.
Other issues with regard to the design of wet disc friction brakes relate to a slip phenomena which occurs as the brake absorbs energy. Generally, the wet disc friction brakes are called "wet" since there is a lubricant supplied to the chambers around the discs. When the vehicle is cold, the lubricant can be viscous, and there may be little slippage between the discs when the brakes are engaged. However, as the vehicle heats, the oil becomes less viscous and there can occur a "slip and stick" phenomena wherein the brakes will first engage, then stick relative to each other, then re-engages. There can be undesirable vibration and heat transmitted to the discs when this occurs.